This invention relates to a pallet changer for changing pallets between a machine tool and a pallet stocker and, more particularly, to a pallet changer of the type having improved operability in changing pallets.
In order to improve the efficiency of mounting and removing work on and from a work table in a numerically controlled machine tool such as a machining center, pallets are used for mounting work. Pallet changers have been used for changing or transporting pallets between a work table and a stocker and also handling pallets in a machine tool. This pallet changer has a pallet support, which is rotatable between the work table of a machine tool and a pallet stocker such as a pallet transporter or a preparation station, at which a work is mounted on and removed from a pallet. A pallet, on which a work to be machined, is transferred from the pallet stocker to the pallet support through one of the inlet/outlets of the pallet support so as to be ready for being transferred to the work table or machine tool. After the machining is completed, the pallet, on which the machined work is mounted, is transferred from the work table of the machine tool to the pallet support through the other inlet/outlet. Subsequently, the pallet support is rotated to transfer the pallet with the machined work mounted thereon to the pallet stocker or change the machined work on the pallet with a new work to be machined while transferring the pallet with the work to be machined to the work table of the machine tool.
In such a prior art pallet changer, when transferring a pallet between the work table and pallet stocker or between the pallet support and machine tool, it is necessary to position the pallet support by stopping the rotation thereof at a position, at which the pallet inlet/outlets of the pallet support face the work table and pallet inlet/outlet of the pallet stocker or machine tool, respectively. For this reason, a positioning mechanism is provided, in which a knock pin is provided such that it can project from and retract into a bed rotatably supporting the pallet support, and a positioning hole, in which the knock pin can be received, is provided in the pallet support at a predetermined position thereof.
For the engagement and disengagement between the receiving hole and knock pin in the positioning mechanism, electric control means is used, in which a controller receives a detection signal provided from detecting means, e.g., a limit switch, for electrically detecting the operation of transferring pallets. By this means, the knock pin is raised and lowered by an exclusive actuator.
However, the pallet changer using such electric control means as noted above, requires electric response time from the transfer of pallet to the start of operation of actuator as well as rather a long time for the start of the actuator. Therefore, the efficiency of the pallet change is inevitably reduced.
Further, in the system using a pallet changer, in addition to change the machined work at the preparation station of the pallet support, it is necessary to transfer the pallet carrying the machined work from the preparation station to the external pallet stocker and receive a new pallet carrying a work to be machined from the pallet stocker. In order to satisfy the above requirements for the pallet changer, it is necessary to newly provide detecting means for detecting the transfer of pallets to be changed at the preparation station of the pallet changer and also change an electric control sequence, which permits rotation of the pallet support as the pallet moved between the machine tool and the pallet support is transferred onto or from the pallet support. This means that it is necessary to change the electric control sequence of permitting the rotation of the pallet support by modifying or changing a sequence control circuit. Therefore, it is impossible to easily obtain the versatility of selecting the function of changing the machined work at the preparation station of the pallet support without transferring pallets, and a function of transferring the pallet with the machined work between the preparation station and external pallet stocker.
Further, some transfer machines include a positioning/releasing unit, which causes an arm rotatably supported on a bed to be rotated upwardly to be held in a predetermined upward position when in use and releases the arm from the upward position to the lower position when the arm no longer needs to be in the upward position. Some other transfer machines are provided with a mechanism for keeping an auxiliary table horizontal with respect to the work table when required. Further transfer machines for supplying articles to be treated to a machine tool or an automatic assembling machine has a very simple construction in which a hook lever for hooking an arm rotatably supported on a bed in a predetermined position is provided on the bed, and the arm is located and released by engaging and disengaging between the hook lever and the arm. With such a structure, however, the hook lever and the arm must be separately operated. Further, since it is necessary to operate the hook lever by a hand, the arm can not be rotated readily and safely if a heavy object is attached to the arm.